Police and municipal officials said the explosion on rue de Treviso was caused by a gas leak.

The Paris prosecutor's office said that the explosion had injured 47 people, including 10 seriously. Rescuers used helicopters to help evacuate some wounded. They picked them up on the square in front of the Paris Opera House and took them to the hospital.

The Spanish Foreign Ministry said that a Spanish woman had also been killed in the blast and that a Spanish couple was being treated at the hospital. Christophe Castaner, the French Interior Minister, said two Paris firefighters were among the dead.

Firefighters responded shortly after 8:30 to the calls for a gas leak at 6 rue de Treviso, at a junction in the ninth arrondissement of the capital, and asked residents to close their gas supply and stay inside. .

But minutes later, a huge explosion broke windows, burned cars and surprised locals who were just starting their day.

Matthieu Croissandeau, a French resident, was parking his scooter in a nearby street when he heard the explosion. The shockwave triggered alarms throughout the neighborhood, he said, and he saw thick smoke flying off.

"While walking down the street, the windows were broken and I saw very distracted people coming to me, some of whom were wearing pajamas or underwear," he said. "It was a real scene of desolation. The car was knocked down by the explosion, the building's facade was destroyed, people were shouting at the windows. "

Mr. Castaner, moved, congratulated the firefighters, telling reporters that they had saved seven people, including a firefighter trapped under the rubble for more than two hours. About 200 firefighters fought the fire and saved people with ladders after the blast.

Remy Heitz, the Paris prosecutor, said the blast had been "patently accidental," telling reporters: "There was first a gas leak and then the firefighters arrived followed by an explosion that caused the fire. "

But Heitz said the investigators were just beginning to investigate the causes of the gas leak and that all the evidence was taken into account.

The explosion took place as Paris and other cities in France faced the ninth week of demonstrations of the "Yellow Vests" movement, once marked by episodes of violence and vandalism in high-end stores. But nothing indicates that Saturday's explosion has anything to do with the protests.

The yellow vests are protesting against the social and economic policies of President Emmanuel Macron, whom they regard as disconnected from their daily needs. But the demonstrations also came to express greater dissatisfaction with the political and media elites.

On Saturday, the biggest events took place in Paris and Bourges, a much smaller city in central France, chosen by some organizers of the event, because it was closer to the regions where many yellow vests live.

In the middle of the afternoon, there were 32,000 demonstrators in France, including 8,000 in Paris, according to the Ministry of the Interior. Although the crowd was mostly peaceful, sporadic clashes erupted in several areas, with police using tear gas and water cannons to disperse protesters.

The damage after the Paris explosion stretched over several blocks, with the blown windows, the debris scattered in the street and the lights still on.

"The shock wave was particularly violent and spread across the four streets of the intersection, about 100 meters," said Éric Moulin, spokesman for the service. fire of Paris.

The explosion occurred on a residential street in a popular Parisian tourist district, with many hotels and attractions nearby, including the Grévin wax museum and the Folies Bergère music hall.

One person wrote on Twitter: "I woke up in the building trembling as if I had never left California … not an earthquake, but an explosion on the street of Treviso, not even a kilometer from me.

"It was staggering to see," said Mr. Croissandeau, the local resident. "There were tourists coming out of their hotels in their bathrobes."

For many witnesses, especially foreign tourists, terrorism was the first explanation we thought about, said Croissandeau.

"In the current context of tensions, whether it is terrorism or violence that Paris has experienced in recent weeks with yellow vests, everyone is comfortable," he said. "But there was no panic or panic, just amazement and sadness to learn that there were victims."

Anne Hidalgo, mayor of Paris, said that anyone who had been affected by the blast, who needed shelter or who were looking for information about the blast could ask for the same. help to the mayor of the Ninth arrondissement.

Many Parisian buildings use gas for heating and other purposes, but lethal explosions due to leakage are rare. In 2016, an explosion caused by a gas leak in the sixth district tore the roof of a building and made 17 wounded.